What is the BUN test?

The blood urea nitrogen (BUN) test is a common test to check how well your kidneys are working. It measures the amount of urea nitrogen in your blood. Nitrogen is a chemical made by your body when you digest food. Nitrogen combines with other things to form urea, which is body waste that is carried by the blood to the kidneys. The kidneys filter the urea nitrogen out of the blood and into the urine.

Why is it done?

This test is done to help diagnose kidney problems or to check how well treatment of kidney disease is working.

Some medicines are processed by the kidneys and can cause kidney damage as a side effect. Some medical conditions can also cause kidney damage. The BUN test may be done to be sure you have normal kidney function before you start taking these medicines or to check the effect of your medical condition on your kidneys.

This test is almost always done with another test called the creatinine test. Creatinine is a waste product that is made when another chemical, creatine, is broken down to produce energy for the muscles. This waste product is carried by the blood to the kidneys, which filter it from the body into the urine.

How do I prepare for this test?

You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your healthcare provider knows about any medicines, herbs, or supplements that you are taking. Ask your provider before you stop taking any of your regular medicines.

Talk to your healthcare provider if you have any questions.

How is the test done?

Having this test will take just a few minutes. A small amount of blood is taken from a vein in your arm with a needle. The blood is collected in tubes and sent to a lab.

Ask your healthcare provider when and how you will get the result of your test.

What does the test result mean?

Your BUN level may be higher than normal because:

• Your kidneys are not working well.
• You have not been drinking enough fluids to replace fluid you have lost through blood loss, sweat, or urine.
• You have been eating a high-protein diet.
• You have bleeding into your stomach or intestine (from an ulcer, for example).
• You have heart failure or you have had a heart attack.
• You are in shock from burns or an accident.
• You have something blocking the flow of urine, such as an enlarged prostate gland or a kidney stone.
• You are taking a medicine that affects your BUN level.

If you are not sick, a BUN level lower than normal is usually not a cause for concern. If your BUN is lower than normal, it may mean:

• You are drinking a lot more fluids than are needed to replace fluid you have lost through sweat or urine.
• You are not getting the nutrients your body needs.
• Your liver isn’t working well.

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about your result and ask questions, such as:

• If you need more tests
• What kind of treatment you may need
• What lifestyle, diet, or other changes you might need to make